CustomTkinter(python) I cannot put a label inside of a frame that is inside a TopLevel window

Question

Using Custom Tkinter python I have put a label inside of a frame that is inside of a TopLevel Window. The frame can be inside of said window but when I try the label inside of the frame, the label appears on the main window.

def OpenMessageScreen(client):
    #exec(client + " = tk.CTkToplevel(window) ")
    evrenacar = tk.CTkToplevel(window)
    #exec(client + "Frame123 = tk.CTkFrame(master =" +client +",width=300).pack()")
    evrenacarFrame123 = tk.CTkFrame(master = evrenacar,width=300).pack()
    exec(client + "Label = tk.CTkLabel(master=" + client + "Frame123,text = \'test\').pack()")
    evrenacarLabel = tk.CTkLabel(master=evrenacar.frame("evrenacarFrame123"),text="merhana")
    evrenacarLabel.pack()  


MessageTestButton = tk.CTkButton(master=MessageFrame,command=lambda: OpenMessageScreen("evrenacar")).pack()

MessageFrame is just a frame on the Main Window, and evrenacar is the client name (just a variable name not important).

And if you are wondering about the commentary sections and replaced variable versions with the same code on the function. That's just a test to make sure exec() is not the cause of this problem. (it is not)

I have created a Toplevel window that activates using a button. When the button is pressed, it has a command that names the top level window as the lamba function below, that using that variable client, it can produce more then one windows(the exec function that creates more then one window isn't the problem). The window works fine, and I have put a frame inside of it. But when I try putting a label inside of said frame, the label appears on the main window. Can you help me solve this bug.

Answer 1

Consider this line of code:

evrenacarFrame123 = tk.CTkFrame(master = evrenacar,width=300).pack()

If you examine evrenacarFrame123 you would see that it's None. When you use None (or a variable set to None) as the master of a widget, that widget will appear in the root window.

Why is evrenacarFrame123 set to None? In python, foo = x().y() always sets foo to the return value of .y(). In tkinter, pack() always returns None, so SomeWidget(...).pack() will always return None.

The solution is to separate the creation of the widget from the layout.

evrenacarFrame123 = tk.CTkFrame(master = evrenacar,width=300)
evrenacarFrame123.pack()

If you want to prevent creating a widget in the root window in case of specification of None as a master of the widget, you can call the function NoDefaultRoot() in the tkinter module to turn this default behavior off.

After calling NoDefaultRoot() you will get the error message RuntimeError: No master specified and tkinter is configured to not support default root if you have passed None as a master widget when creating a new widget.

Answer 2

For the sake of completeness to give an example how NoDefaultRoot() works while using default tkinter module (see the answer by Bryan Oakley) run the code below:

import tkinter as tk

# ===== ===== ===== ===== ===== ===== ===== ===== ===== ===== 
root       = tk.Tk()
toplevelWindow = tk.Toplevel(root)
tk.Label(master=toplevelWindow, text="toplevelWindow:  Label-Toplevel").pack()
tk.Label(master=None,           text="master=None: Label-Root").pack()
root.mainloop()


# ===== ===== ===== ===== ===== ===== ===== ===== ===== ===== 
tk.NoDefaultRoot()
root       = tk.Tk()
toplevelWindow = tk.Toplevel(root)
tk.Label(master=toplevelWindow, text="toplevelWindow:  Label-Toplevel").pack()
tk.Label(master=None,           text="master=None: Label-Root").pack()
root.mainloop()

to experience both, creation of a widget in the root window and the error message raised while using tk.NoDefaultRoot().